Prepare draft

1 files changed, 110 insertions, 0 deletions

diff --git a/_drafts/bird-cpu-usage.md b/_drafts/bird-cpu-usage.md
new file mode 100644
index 0000000..136a475
--- /dev/null
+++ b/_drafts/bird-cpu-usage.md
@@ -0,0 +1,110 @@
+---
+layout: post
+title: Bird CPU usage
+date: 2025-01-07 19:06 +0100
+categories: tech
+lang: en
+---
+
+Several times already, I noticed this in my Munin monitoring:
+
+{% image
+img="https://pics.uvokchee.de/upload/2025/01/07/20250107180512-c1453895.png"
+alt="RRD tool graphic showing a high CPU usage" %}
+
+I found it strange, but had no time to inspect further.
+
+Recently, I tried to investigate what happens on the server there.
+htop showed high CPU usage for both bird and dnsmasq (always
+together) in these times.
+
+Fuming a bit, I went with a brute-force approach:
+
+```
+#!/bin/bash
+
+# Configuration
+THRESHOLD=1.0
+# 3 hours
+DURATION=$((3*80*80))
+MAIL_TO="lolnope"
+SUBJECT="High Load Average Alert"
+BODY="The load average has been above ${THRESHOLD} for more than 3 hours."
+REBOOT_CMD="/sbin/reboot"
+
+# Function to check the load average
+check_load() {
+    # 15 min loadavg
+    loadavg=$(awk '{print $3}' /proc/loadavg)
+    echo "$(date): Current Load Average: $loadavg"
+
+    if (( $(echo "$loadavg > $THRESHOLD" | bc -l) )); then
+        echo "$(date): Load average is above threshold."
+        return 0
+    else
+        echo "$(date): Load average is below threshold."
+        return 1
+    fi
+}
+
+# Monitor the load average
+start_time=$(date +%s)
+while true; do
+    if check_load; then
+        current_time=$(date +%s)
+        elapsed_time=$((current_time - start_time))
+
+        if [ "$elapsed_time" -gt "$DURATION" ]; then
+            echo "$(date): Load average has been above threshold for more than 3 hours."
+
+            # Send alert email
+            (echo "$BODY"; ps -e -o %cpu,%mem,cmd --sort pcpu | tail) | mail -s "$SUBJECT" "$MAIL_TO"
+
+            # Reboot the server
+#            systemctl stop bird
+#            systemctl start bird
+            $REBOOT_CMD
+            break
+        fi
+    else
+        start_time=$(date +%s)
+    fi
+    sleep 300 # Check every 5 minutes
+done
+
+```
+
+Specifically, the output of ps
+
+```
+22.7  2.7 /usr/sbin/bird -f -u bird -g bird
+33.3  0.1 ps -e -o %cpu,%mem,cmd --sort pcpu
+37.4  0.0 /usr/sbin/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new,.bak --local-service --trust-anchor=.,20326,8,2,e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
+```
+
+confirmed the suspicion - although the "percentage" is a bit weird. From the
+manpage:
+
+> Currently, it is the CPU time used divided by the time the process has been
+> running (cputime/realtime ratio), expressed as a percentage.
+
+(So if the process runs "long enough" and only starts misbehaving after a year,
+it won't show up?).
+
+I asked an LLM what to do, in addition to strace, and it suggested perf.
+Unfortunately, this requires debug symbols [1]. [And while Debian does provide
+debug symbols](https://wiki.debian.org/HowToGetABacktrace) - it doesn't for
+dnsmasq (yet) in bookworm.  Luckily, the nice people at labs.nic.cz provide a
+dbgsym package in their Bird(2) Debian repository.
+
+Now, stracing dnsmasq (when "idle") reveals some recvmsg of type `RTM_NEWROUTE`.
+I have *no idea* why dnsmasq would need that. But I already *assume* the high
+CPU usage occurs when Bird exports lots of routes to the kernel.
+
+Also, in journalctl, I see lots of the infamous `Kernel dropped some netlink
+messages, will resync on next scan.` messages at times - the message apparently
+nobody has a solution to, and even though there are mailing list posts telling
+to sysctl `net.core.rmem_default`, I doesn't seem to yield a solution.
+
+[1] At least when I want to see the binaries function names.
+  Kernel symbols seem to show up fine.